Essential amino acid mixtures drive cancer cells to apoptosis through proteasome inhibition and autophagy activation.

Cancer cells require both energy and material to survive and duplicate in a competitive environment. Nutrients, such as amino acids (AAs), are not only a caloric source, but can also modulate cell metabolism and modify hormone homeostasis. Our hypothesis is that the environmental messages provided by AAs rule the dynamics of cancer cell life or death, and the alteration of the balance between essential amino acids (EAAs) and non-essential amino acids (NEAAs) (lower and higher than 50%, respectively) present in nutrients may represent a key instrument to alter environment-dependent messages, thus mastering cancer cells destiny. In this study, two AA mixtures, one exclusively consisting of EAAs and the other consisting of 85% EAAs and 15% NEAAs, were tested to explore their effects on the viability of both normal and cancer cell lines and to clarify the molecular mechanisms involved. Both mixtures exerted a cell-dependent anti-proliferative, cytotoxic effect involving the inhibition of proteasome activity and the consequent activation of autophagy and apoptosis. These results, besides further validating the notion of the peculiar interdependence and extensive crosstalk between the ubiquitin-proteasome system (UPS) and autophagy, indicate that variation in the ratio of EAAs and NEAAs can deeply influence cancer cell survival. Consequently, customization of dietary ratios among EAAs and NEAAs by specific AA mixtures may represent a promising anticancer strategy able to selectively induce death of cancer cells through the induction of apoptosis via both UPS inhibition and autophagy activation.

SIRT6 Is a Positive Regulator of Aldose Reductase Expression in U937 and HeLa cells under Osmotic Stress: In Vitro and In Silico Insights.

SIRT6 is a protein deacetylase, involved in various intracellular processes including suppression of glycolysis and DNA repair. Aldose Reductase (AR), first enzyme of polyol pathway, was proposed to be indirectly associated to these SIRT6 linked processes. Despite these associations, presence of SIRT6 based regulation of AR still remains ambiguous. Thus, regulation of AR expression by SIRT6 was investigated under hyperosmotic stress. A unique model of osmotic stress in U937 cells was used to demonstrate the presence of a potential link between SIRT6 and AR expression. By overexpressing SIRT6 in HeLa cells under hyperosmotic stress, its role on upregulation of AR was revealed. In parallel, increased SIRT6 activity was shown to upregulate AR in U937 cells under hyperosmotic milieu by using pharmacological modulators. Since these modulators also target SIRT1, binding of the inhibitor, Ex-527, specifically to SIRT6 was analyzed in silico. Computational observations indicated that Ex-527 may also target SIRT6 active site residues under high salt concentration, thus, validating in vitro findings. Based on these evidences, a novel regulatory step by SIRT6, modifying AR expression under hyperosmotic stress was presented and its possible interactions with intracellular machinery was discussed.

Kinetic properties of Streptomyces canarius L- Glutaminase and its anticancer efficiency

Abstract L-glutaminase was produced by Streptomyces canarius FR (KC460654) with an apparent molecular mass of 44 kDa. It has 17.9 purification fold with a final specific activity 132.2 U/mg proteins and 28% yield recovery. The purified L-glutaminase showed a maximal activity against L-glutamine when incubated at pH 8.0 at 40 °C for 30 min. It maintained its stability at wide range of pH from 5.0 11.0 and thermal stable up to 60 °C with Tm value 57.5 °C. It has high affinity and catalytic activity for L-glutamine (Km 0.129 mM, Vmax 2.02 U/mg/min), followed by L-asparagine and L-aspartic acid. In vivo, L-glutaminase showed no observed changes in liver; kidney functions; hematological parameters and slight effect on RBCs and level of platelets after 10 days of rabbit's injection. The anticancer activity of L-glutaminase was also tested against five types of human cancer cell lines using MTT assay in vitro. L-glutaminase has a significant efficiency against Hep-G2 cell (IC50, 6.8 μg/mL) and HeLa cells (IC50, 8.3 μg/mL), while the growth of MCF-7 cells was not affected. L-glutaminase has a moderate cytotoxic effect against HCT-116 cell (IC50, 64.7 μg/mL) and RAW 264.7 cell (IC50, 59.3 μg/mL).

AMP-activated protein kinase is required for cell survival and growth in HeLa-S3 cells in vivo.

Activation of the AMP-dependent protein kinase (AMPK) is linked to cancer cell survival in a variety of cancer cell lines, particularly under conditions of stress. As a potent activator of AMPK, metformin has become a hot topic of discussion for its effect on cancer cell. Here, we report that AMPK activated by metformin promotes HeLa-S3 cell survival and growth in vivo. Our results show that metformin inhibited cell proliferation in MCF-7 cells, but not in LKB1-deficient HeLa-S3 cells. Re-expression of LKB-1 in HeLa-S3 cells restored the growth inhibitory effect of metformin, indicating a requirement for LKB-1 in metformin-induced growth inhibition. Moreover, AMPK activation exerted a protective effect in HeLa-S3 cells by relieving ER stress, modulating ER Ca(2+) storage, and finally contributing to cellular adaptation and resistance to apoptosis. Our findings identify a link between AMPK activation and cell survival in HeLa-S3 cells, which demonstrates a beneficial effect of AMPK activated by metformin in cancer cell, and suggests a discrete re-evaluation on the role of metformin/AMPK activation on tumor cell growth, proliferation, and on clinical application in cancer therapy.

Lipid-based nanoparticles as nonviral gene delivery vectors.

Efficient delivery of nucleic acids into cells is a promising technique to modulate cellular gene expression for therapeutic and research applications. Cationic lipid-based liposomes represent one of the most intensively studied and employed nonviral vectors. They are positively charged at physiological pH and spontaneously self-assemble with polyanionic nucleic acids forming nanoscaled complexes named lipoplexes. Here, we draft a simple protocol for the development, characterization, optimization, and screening of liposomal formulations for in vitro gene delivery. In particular, we report as a practical example a quick method to formulate and extrude nanometer-sized unilamellar cationic vesicles composed of DOTAP as cationic lipid and DOPE as zwitterionic helper lipid at 1:1 molar ratio. The physico-chemical characterization of liposomes and lipoplexes involves the measurement of mean diameter and overall surface charge using Dynamic Light Scattering (DLS) and Laser Doppler Microelectrophoresis. The outlined transfection procedure takes into account several experimental parameters affecting the in vitro performance of gene delivery systems, paying special attention to the charge ratio (CR). Gene delivery effectiveness is evaluated both in terms of transfection efficiency and cytotoxicity of the vector to find the optimal transfection conditions. Importantly, the proposed protocol can be easily shifted to different types of nonviral vectors.

Increased concentration of sialidases by HeLa cells might influence the cytotoxic ability of NK cells.

OBJECTIVE: Cancer cells reportedly have the ability to escape from the immune system, mainly from natural killer (NK) cells. Although the real mechanisms are complicated, some inhibitors that are secreted from the cancer cells might play an important role. This study's aim was to investigate the potential mediator released by cancer cells (HeLa) that contributes to the decreased cytotoxicity of NK cells. METHODS AND MATERIALS: An NK-HeLa coculture system was used to test the hypothesis that the presence of the potential mediator from cancer cells contributes to the decreased cytotoxicity of NK cells. RESULTS: After coculturing with HeLa cancer cells, the cytotoxicity of NK cells was decreased. When the coculture medium and culture medium containing commercialized sialidase were used to culture NK cells, the cytotoxicity of the NK cells was also inhibited. However, cytotoxicity was partially restored by a sialidase inhibitor (DANA). Western blot analysis of the HeLa cells after coculturing with NK cells demonstrated increased Neu2 and Neu3 expression in HeLa cells. CONCLUSIONS: The finding that Neu2 and Neu3 expression in cancer cells might be involved in the impaired function of NK cells, which could be restored by a sialidase inhibitor, provides a new concept that could be applied to the management of cancer.

Capsaicin, a component of red peppers, stimulates protein kinase CKII activity.

Protein kinase CKII (CKII), a heterotetramer composed of two catalytic (alpha or alpha') subunits and two regulatory (beta) subunits, plays a critical role in cell proliferation and anti-apoptosis. Recently, capsaicin was shown to trigger apoptosis. Therefore, we examined the effect of capsaicin on CKII activity. Although capsaicin induced apoptotic death in HeLa cells, CKII activity was increased in the cytosolic fraction of HeLa cells after treatment. Capsaicin did not change the expression of the CKIIalpha and CKIIbeta proteins. Capsaicin stimulated the catalytic activity of recombinant CKII tetramer, but not the CKIIalpha subunit. Moreover, capsaicin enhanced the autophosphorylation of CKIIalpha and CKIIbeta. Taken together, our data suggest that capsaicin stimulates the phosphotransferase activity of CKII holoenzyme by interacting with the CKIIbeta subunit.

A new nuclear protease with cathepsin L properties is present in HeLa and Caco-2 cells.

Recently many authors have reported that cathepsin L can be found in the nucleus of mammalian cells with important functions in cell-cycle progression. In previous research, we have demonstrated that a cysteine protease (SpH-protease) participates in male chromatin remodeling and in cell-cycle progression in sea urchins embryos. The gene that encodes this protease was cloned. It presents a high identity sequence with cathepsin L family. The active form associated to chromatin has a molecular weight of 60 kDa, which is higher than the active form of cathepsin L described until now, which range between 25 and 35 kDa. Another difference is that the zymogen present in sea urchin has a molecular weight of 75 and 90 kDa whereas for human procathepsin L has a molecular weight of 38-42 kDa. Based on these results and using a polyclonal antibody available in our laboratory that recognizes the active form of the 60 kDa nuclear cysteine protease of sea urchin, ortholog to human cathepsin L, we investigated the presence of this enzyme in HeLa and Caco-2 cells. We have identified a new nuclear protease, type cathepsin L, with a molecular size of 60 kDa, whose cathepsin activity increases after a partial purification by FPLC and degrade in vitro histone H1. This protease associates to the mitotic spindle during mitosis, remains in the nuclei in binuclear cells and also translocates to the cytoplasm in non-proliferative cells.

Establishment of a simple detection system for blood group ABO-specific transferase activity in DNA-transfected cells.

A/B-transferase is a glycosyltransferase that transfers a sugar substrate onto H-antigen resulting in the synthesis of glycoproteins and glycolipids termed A/B-antigens. The ABO blood group (ABO) gene encoding A/B-transferase possesses numerous polymorphisms affecting the specificity and/or activity of the enzyme. The relationship between genotype and phenotype is very complicated, except for those of some critical polymorphisms. In order to establish a system for evaluating the effect of each polymorphism on the transferase function, an A- or B-transferase cDNA expressing vector was introduced into HeLa cells, a cell line that do not possess endogenous A/B-transferase activity. We successfully detected substrate-specific transferase activity in the cells and in the culture medium. Furthermore, in three different assays, each corresponding A- or B-antigen was detected in the transfectants with high sensitivity. Accordingly, the present study demonstrates a possibility that A/B-transferase variants may be characterized by using this method.

The integrator complex recognizes a new double mark on the RNA polymerase II carboxyl-terminal domain.

The carboxyl-terminal domain (CTD) of the largest subunit of RNA polymerase II (pol II) comprises multiple tandem repeats of the heptapeptide Tyr(1)-Ser(2)-Pro(3)-Thr(4)-Ser(5)-Pro(6)-Ser(7). This unusual structure serves as a platform for the binding of factors required for expression of pol II-transcribed genes, including the small nuclear RNA (snRNA) gene-specific Integrator complex. The pol II CTD specifically mediates recruitment of Integrator to the promoter of snRNA genes to activate transcription and direct 3' end processing of the transcripts. Phosphorylation of the CTD and a serine in position 7 are necessary for Integrator recruitment. Here, we have further investigated the requirement of the serines in the CTD heptapeptide and their phosphorylation for Integrator binding. We show that both Ser(2) and Ser(7) of the CTD are required and that phosphorylation of these residues is necessary and sufficient for efficient binding. Using synthetic phosphopeptides, we have determined the pattern of the minimal Ser(2)/Ser(7) double phosphorylation mark required for Integrator to interact with the CTD. This novel double phosphorylation mark is a new addition to the functional repertoire of the CTD code and may be a specific signal for snRNA gene expression.

Quinolinate phosphoribosyl transferase, a key enzyme in de novo NAD(+) synthesis, suppresses spontaneous cell death by inhibiting overproduction of active-caspase-3.

Quinolinate phosphoribosyl transferase (QPRT) is a key enzyme in de novo NAD(+) synthesis. QPRT enzyme activity has a restricted tissue distribution, although QPRT mRNA is expressed ubiquitously. This study was designed to elucidate the functions of QPRT protein in addition to NAD(+) synthesis. QPRT was identified as a caspase-3 binding protein using double layer fluorescent zymography, but was not a substrate for caspase-3. Surface plasmon resonance analysis using recombinant proteins showed interaction of QPRT with active-caspase-3 in a dose dependent manner at 55 nM of the dissociation constant. The interaction was also confirmed by immunoprecipitation analysis of actinomycin D-treated QPRT-FLAG expressing cells using anti-FLAG-agarose. QPRT-depleted cells showed increased sensitivity to spontaneous cell death, upregulated caspase-3 activity and strong active-caspase-3 signals. Considered together, the results suggested that QPRT protein acts as an inhibitor of spontaneous cell death by suppressing overproduction of active-caspase-3.

A novel functional element in the N-terminal region of Arum concinnatum alternative oxidase is indispensable for catalytic activity of the enzyme in HeLa cells.

Alternative oxidase (AOX) is a quinol-oxygen oxidoreductase, which is known to possess a dicarboxylate diiron reaction center held in structurally postulated alpha-helical bundle. However, little is known about the structural or functional features of its N-terminal region in any organism, with the exception of a regulatory cysteine residue (CysI) in angiosperm plants. Here, we show that transcripts of two AOX1 isozymes (AcoAOX1a and AcoAOX1b) are coexpressed in thermogenic appendices of Arum concinnatum, while their enzymatic activities seem to be distinct. Namely, AcoAOX1a, an abundantly expressed transcript in vivo, shows an apparent cyanide-insensitive and n-propyl gallate-sensitive respiration during ectopic expression of the protein in HeLa cells, whereas AcoAOX1b exhibits a lower transcript expression, and appears to be totally inactive as AOX at the protein level. Our functional analyses further reveal that an E83K substitution in AcoAOX1b, which is located far upstream of CysI in the N-terminal region, is the cause of this loss of function. These results suggest the presence of a naturally occurring inactive AOX homologue in thermogenic plants. Accordingly, our results further imply that the N-terminal region of the AOX protein functionally contributes to the dynamic activities of respiratory control within the mitochondria.

Bystander effect from cytosine deaminase and uracil phosphoribosyl transferase genes in vitro: a partial contribution of gap junctions.

Among gene therapy strategies elaborated to kill cancer cells, one uses the CodA gene, coding for cytosine deaminase (CD) that converts 5-fluorocytosine (5-FC) into toxic 5-fluorouracil (5-FU). To enhance 5-FC metabolic activation, we prepared a vector carrying CodA and upp (uracil phosphoribosyl transferase) genes which rendered HeLa cells sensitive to 5-FC and enhanced a bystander effect not mediated by gap junctions. However, 1% CD(+)-UPP(+) cells were able to kill 40% of the cell population if the cells were communicating. This suggests that, at very low percentages of CD(+)-UPP(+) cells, CodA and upp induce a bystander effect through gap junction-dependent mechanisms.

Acquired vorinostat resistance shows partial cross-resistance to 'second-generation' HDAC inhibitors and correlates with loss of histone acetylation and apoptosis but not with altered HDAC and HAT activities.

Histone deacetylase (HDAC) inhibitors such as vorinostat (suberoylanilide hydroxamic acid), valproic acid, romidepsin (FK-228), and LBH589 comprise a relatively new class of potent anticancer agents. This study provides evidence for the potential of vorinostat to cause acquisition of multidrug resistance protein-independent resistance in HCT116 colon tumor cells. This acquired resistance is moderate (two-fold to three-fold), is nonreversible, and correlates with the loss of responses typically seen with HDAC inhibitors, that is the loss of acetylation of the histones H2A, H2B, H3, and H4, the loss of the G2/M checkpoint activation, and the loss of caspase 3-dependent and caspase 7-dependent apoptosis. This acquired resistance also associates with cross-resistance to the hydroxamate-class (LBH589 and JNJ26481585) and to the aliphatic acid-class (valproic acid) HDAC inhibitors but not to the benzamide-class (MGCD0103) and the cyclic peptide-class (romidepsin) HDAC inhibitors. The acquired HDAC inhibitor resistance described hereis not a result of altered HDAC and histone acetyltransferase activities and differs from that previously reported for romidepsin.

A high throughput, whole cell screen for small molecule inhibitors of the mitotic spindle checkpoint identifies OM137, a novel Aurora kinase inhibitor.

In mitosis, the kinetochores of chromosomes that lack full microtubule attachments and/or mechanical tension activate a signaling pathway called the mitotic spindle checkpoint that blocks progression into anaphase and prevents premature segregation of the chromatids until chromosomes become aligned at the metaphase plate. The spindle checkpoint is responsible for arresting cells in mitosis in response to chemotherapeutic spindle poisons such as paclitaxel or vinblastine. Some cancer cells show a weakened checkpoint signaling system that may contribute to chromosome instability in tumors. Because complete absence of the spindle checkpoint leads to catastrophic cell division, we reasoned that drugs targeting the checkpoint might provide a therapeutic window in which the checkpoint would be eliminated in cancer cells but sufficiently preserved in normal cells. We developed an assay to identify lead compounds that inhibit the spindle checkpoint. Most cells respond to microtubule drugs by activating the spindle checkpoint and arresting in mitosis with a rounded morphology. Our assay depended on the ability of checkpoint inhibitor compounds to drive mitotic exit and cause cells to flatten onto the substrate in the continuous presence of microtubule drugs. In this study, we characterize one of the compounds, OM137, as an inhibitor of Aurora kinases. We find that this compound is growth inhibitory to cultured cells when applied at high concentration and potentiates the growth inhibitory effects of subnanomolar concentrations of paclitaxel.

Induction of apoptosis by the inhibitors of poly(ADP-ribose)polymerase in HeLa cells.

To investigate the role of poly(ADP-ribose)polymerase (PARP) in the physiological condition of cell growth, we studied the ability of PARP inhibitors to induce apoptosis. Benzamide (BA) and 4-amino-1,8-naphthalimide (NAP), two well-known inhibitors of PARP, treatment increased nuclear fragmentation and caspase-3 activity in HeLa (Human cervical cancer cell line) cells. The increase of cellular NAD(+) level was observed in HeLa cells treated with BA in comparison with untreated control cells. For unrevealing the specific PARP family member responsible for such induction of apoptosis we knocked down and over-expressed PARP-1 gene in HeLa cells. PARP-1 knock down cells were sensitive to BA induced nuclear fragmentation and caspase-3 activation while exogenous expression of PARP-1 rendered cells resistant to BA induced apoptosis. This result indicated that inhibition of PARP-1 resulted in induction of apoptosis.

The large form of human 2',5'-Oligoadenylate Synthetase (OAS3) exerts antiviral effect against Chikungunya virus.

Chikungunya virus (CHIKV) becomes one of the most important mosquito-borne alphavirus in the medical field. CHIKV is highly sensitive to antiviral activity of Type-I interferons (IFN-alpha/beta). Here, we investigated the role of IFN-induced 2',5'-Oligoadenylate Synthetase (OAS) family in innate immunity to CHIKV. We established inducible human epithelial HeLa cell lines expressing either the large form of human OAS, OAS3, or the genetic variant OAS3-R844X which is predicted to lack about 20% of the OAS3 protein from the carboxy terminus. HeLa cells respond to ectopic OAS3 expression by efficiently inhibiting CHIKV growth. The characteristic of the antiviral effect was a blockade in early stages of virus replication. Thus, OAS3 pathway may represent a novel antialphaviral mechanism by which IFN-alpha/beta controls CHIKV growth. HeLa cells expressing the truncated form of OAS3 were less resistant to CHIKV infection, raising the question on the involvement of OAS3 genetic polymorphism in human susceptibility to alphavirus infection.

Evaluation of cytotoxic, genotoxic and CYP450 enzymatic competition effects of Tanzanian plant extracts traditionally used for treatment of fungal infections.

HIV-infected patients in sub-Saharan countries highly depend on traditional medicines for the treatment of opportunistic oral infections as candidiasis. Previous investigations on antifungal activity of medicinal plant extracts utilized by traditional healers in Tanzania have revealed 12 extracts with potent antifungal activity. Although the plants may be good candidates for new treatment opportunities, they can be toxic or genotoxic and could cause pharmacokinetic interactions when used concomitantly with antiretroviral agents. Therefore, we investigated the cytotoxicity, genotoxicity and cytochrome P450 interaction potential of these medicinal plants. Cytotoxicity was tested by Hoechst 33342, Alamar Blue, calcein-AM, glutathione depletion and O(2)-consumption assays and genotoxicity by a Vitotox assay. Competition of the 12 extracts on substrate metabolism by CYP3A4, 2C9, 2C19 and 2D6 was tested with high-throughput CYP inhibition screening. Pregnane X receptor (PXR) activation was tested using Chinese hamster ovary cell lines expressing human PXR. Herbal extracts inducing high human PXR activation were tested for enhanced CYP3A4 mRNA levels with quantitative polymerase chain reaction. Genotoxicity was found for Jatropha multifida, Sterculia africana and Spirostachys africana. All plant extracts showed high cytotoxic effects in almost all tests. Potent competition with CYP3A4, 2D6, 2C9 and 2C19 was found for 75% of the herbal extracts. Spirostachys africana did not affect CYP2D6 and for S. africana and Turraea holstii no effect on CYP2D6 and CYP3A4 (DBF) was found. Nine plant extracts showed significant activation of human PXR, but only Agaura salicifolia, Turraea holstii and S. africana significantly induced CYP3A4 mRNA levels. These results indicate the possibility of potential medicinal plant-antiretroviral interactions.

Phosphorylation of LKB1 at serine 428 by protein kinase C-zeta is required for metformin-enhanced activation of the AMP-activated protein kinase in endothelial cells.

BACKGROUND: Metformin, one of most commonly used antidiabetes drugs, is reported to exert its therapeutic effects by activating AMP-activated protein kinase (AMPK); however, the mechanism by which metformin activates AMPK is poorly defined. The objective of the present study was to determine how metformin activates AMPK in endothelial cells. METHODS AND RESULTS: Exposure of human umbilical vein endothelial cells or bovine aortic endothelial cells to metformin significantly increased AMPK activity and the phosphorylation of both AMPK at Thr172 and LKB1 at Ser428, an AMPK kinase, which was paralleled by increased activation of protein kinase C (PKC)-zeta, as evidenced by increased activity, phosphorylation (Thr410/403), and nuclear translocation of PKC-zeta. Consistently, either pharmacological or genetic inhibition of PKC-zeta ablated metformin-enhanced phosphorylation of both AMPK-Thr172 and LKB1-Ser428, suggesting that PKC-zeta might act as an upstream kinase for LKB1. Furthermore, adenoviral overexpression of LKB1 kinase-dead mutants abolished but LKB1 wild-type overexpression enhanced the effects of metformin on AMPK in bovine aortic endothelial cells. In addition, metformin increased the phosphorylation and nuclear export of LKB1 into the cytosols as well as the association of AMPK with LKB1 in bovine aortic endothelial cells. Similarly, overexpression of LKB1 wild-type but not LKB1 S428A mutants (serine replaced by alanine) restored the effects of metformin on AMPK in LKB1-deficient HeLa-S3 cells, suggesting that Ser428 phosphorylation of LKB1 is required for metformin-enhanced AMPK activation. Moreover, LKB1 S428A, like kinase-dead LKB1 D194A, abolished metformin-enhanced LKB1 translocation as well as the association of LKB1 with AMPK in HeLa-S3 cells. Finally, inhibition of PKC-zeta abolished metformin-enhanced coimmunoprecipitation of LKB1 with both AMPKalpha1 and AMPKalpha2. CONCLUSIONS: We conclude that PKC-zeta phosphorylates LKB1 at Ser428, resulting in LKB1 nuclear export and hence AMPK activation.

DEVD-NucView488: a novel class of enzyme substrates for real-time detection of caspase-3 activity in live cells.

Live-cell detection of intracellular enzyme activity requires that substrates are cell-permeable and that the generated products are easily detected and retained in cells. Our objective was to create a novel fluorogenic substrate that could be used for real-time detection of apoptosis in living cells. We have synthesized a highly cell-permeable caspase-3 substrate, DEVD-NucView488, by linking a fluorogenic DNA-binding dye to the caspase-3 recognition sequence that renders the dye nonfunctional. On substrate cleavage, the dye is released and becomes highly fluorescent on binding to DNA. DEVD-NucView488 detected caspase-3 activation within a live-cell population much earlier and with higher sensitivity compared with other apoptosis reagents that are currently available. Furthermore, cells incubated with DEVD-NucView488 exhibited no toxicity and normal apoptotic progression. DEVD-NucView488 is an ideal substrate for kinetic studies of caspase-3 activation because it detects caspase-3 activity in real-time and also efficiently labels DNA in nuclei of caspase-3-activated cells for real-time fluorescent visualization of apoptotic morphology. The strategy utilized in the design of this fluorogenic substrate can be applied in future endeavors to develop substrates for detecting real-time intracellular enzyme activity.